AI is irrelevant to the reason why there isn't a written version of every single national dialect of sign language. The reason it doesn't exist is because it would serve no purpose (source: many deaf friends). Deaf communities learn the country's writing system just like everyone else.

The closest thing out there is SignWriting [1] which has about as much traction in the real world as esperanto.

https://en.wikipedia.org/wiki/SignWriting